In an HVAC system, controllers or control circuits are coupled between a system thermostat and a heating or cooling device. The controller receives signals from the system thermostat and controls the heating or cooling device in response to the signals from the system thermostats. The controller turns the devices ON and OFF in response to the signals from the system thermostat in order to provide a comfortable temperature regulated environment.
A heating or cooling device or appliance is an HVAC unit. An HVAC unit is any device for providing heating, cooling and/or air circulation. Examples of HVAC units are furnaces for providing hot air, air conditioners for providing cool air, fans for providing air circulation, or other environmental control appliances such as boilers. Preferably, the HVAC unit is a forced air system which is capable of both heating and cooling the environment.
In a forced air system, an air handler (blower, plenums and associated ductwork) moves air from the interior of the HVAC unit to the temperature regulated environment. The air handler may be used with heating and/or cooling units where energy is provided by electricity, gas, oil, as well as other fuels. The blower of the air handler generally includes a fan which is turned by an electric motor. In a forced air system such as a heating furnace, the blower forces hot air produced by a gas flame or electric coil to the environment. In a forced air system such as an air conditioner, the blower forces cool air produced by cooling coils and a compressor to the environment.
The blower in the air handler often is automatically turned ON when the HVAC unit is turned ON. Most HVAC units include start-up controls which do not turn ON the motor in the blower immediately after the HVAC unit is turned ON. These start-up controls delay the operation of the blower for a predetermined time or until a specific temperature is reached within the HVAC unit. The blower may also be turned ON by providing an external blower signal to the HVAC unit. Turning the blower ON with an external blower signal is referred to as forcing the blower ON. Proper blower operation is critical to effective HVAC unit operation because operating a HVAC unit with a malfunctioning blower may cause damage to the HVAC unit and waste energy.
Medium-sized buildings and rooms such as store fronts, light commercial buildings, or other facilities are generally heated and cooled by a number of small HVAC units operating in parallel because HVAC units of today have smaller heating and cooling capacities. Although smaller HVAC units tend to be more efficient, operating these HVAC units in parallel creates special problems. For example, HVAC units of today are generally controlled by individual thermostats. Operating multiple HVAC units with individual thermostats does not allow cooperation and integration of the individual thermostats and HVAC units.
Therefore, there is a need for a twinning control which can control the operation of two or more HVAC units. Controlling two or more HVAC units with a single twinning control allows more effective heating and cooling, superior fault detection, and more dependable HVAC unit operation, as well as backup operation. Further, a twinning control which allows single mode operation or dual mode operation provides superior flexibility in the HVAC system.